A lot of people will miss this since it's posted on a weekend. If this doesn't make the Monday morning HN front page, I recommend waiting a week or so and reposting as a Show HN some weekday morning.
No...after the first X minutes, the option to change the title is lost. Maybe a mod will change it though.
...and you can always send an email to the mods to ask them to do this - hn@ycombinator.com
They tend to reply quickly and are very helpful, in my experience!